Nbatches, particles when using surf_source_read

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Hi,
Two very basic question that puzzle me:

  1. Why OpenMC uses ‘nbatches’ and ‘particles’ in fixed source mode instead of a single number for the simulated histories (as it is done in MCNP or PHITS)?

  2. How do ‘nbatches’ and ‘particles’ work when surf_source_read is used to read particles from a previously created surface_source.h5 file. In this case, source is not used and it seems that tallies now are normalized to the number of source particles in surface_source.h5 (is it?). How ‘nbatches’ and ‘particles’ numbers are used in this case?